Film

ABSTRACT

The present invention relates to a film, in particular to a laser writable film, and to substances used therein, and components thereof. The present invention further relates to a method of manufacturing the film, uses thereof and products comprising the film.

This application is a continuation application of U.S. patentapplication Ser. No. 14/646,311, filed May 20, 2015, which claimspriority to International Patent Application No. PCT/GB2013/053363,filed Dec. 19, 2013, which claims priority to United Kingdom PatentApplication No. 1222955.5, filed Dec. 19, 2012. The entirety of theaforementioned applications is incorporated herein by reference.

FIELD

The present invention relates to a film, in particular to a laserwritable film, and to substances used therein, and components thereof.The present invention further relates to a method of manufacturing thefilm, uses thereof and products comprising the film.

BACKGROUND

Polymer films are used in many fields for numerous different uses.Countless different properties are required or desirable depending onthe applications in which the films are used. One of the many aestheticand functional characteristics of a film is the presence and nature oftext, images, indicia and other aspects of printed appearance. Thesefunction to provide identifying or other useful information or to give aparticular appearance for visual appeal or other reasons. They are ofparticular use where the film is used in packaging.

Many different techniques can be used for printing or marking films andrelated substrates. Traditionally, substrates have been marked byapplying inks and using various printing techniques. More recently,films have been marked using alternative techniques. One suchalternative technique is laser marking, whereby laser-sensitivecomponents have been applied to or incorporated within substrates suchthat laser irradiation can bring about a change in appearance by causinga change in the laser-sensitive components. Laser marking or writing canbring advantages in terms of cost and performance. The desired mark orimage can be “printed” without ink, merely by “writing” with a laser.Laser writing is precise and quick, and can be used with materials whichare not necessarily flat or uniform. The surfaces of the substrate inmost cases do not have their physical characteristics adversely altered(because they do not come into contact with conventional printingapparatus) and the laser writing techniques may be used even where thelaser-sensitive components are embedded within the substrate.

One example of a laser-sensitive coating composition is disclosed in WO2009/024497. This document discloses a composition comprising titaniumdioxide in the anatase form and a polymeric binder. The document refersto ultra-violet, visible or infra-red laser irradiation, preferablyinfra-red laser irradiation. IR absorbers may also be present, forexample tungsten suboxide, tungsten bronze, or mixtures of tungstentrioxide, tungsten bronze and metallic tungsten.

Amongst chemicals which can change appearance upon irradiation arecertain diacetylene-containing compounds, as disclosed in WO 2009/093028for example. This document discloses diacetylenes which are polychromic, i.e. which change colour upon irradiation. The polychromicdiacetylenes may be present in or on a material so that colour may beimparted to the material, or the colour of the material may be changedupon irradiation. The document discloses that preferred compounds arethose which are initially colourless or of low visual colour and whichbecome coloured upon irradiation, and/or compounds which undergomultiple colour changes. For example, the compounds may change frombeing initially colourless or of low visual colour to become colouredupon irradiation and subsequently to change to a different colour uponfurther irradiation with the same or different type of radiation. Typesof radiation include laser or non-coherent, broadband or monochromaticradiation, ultra-violet, near, mid or far infra-red, visible, microwave,gamma-ray, x-ray or electron beam radiation. The document disclosesthat, in addition to the diacetylene compounds, there may also beincorporated other compounds which undergo colour change reactions onirradiation, for example “leuco dyes”. The document discloses that thepoly chromic substances may be included in a surface coating formulationor within the bulk of the substrate. The substrates can includethermoplastics.

WO 2009/081385 also discloses diacetylene-containing poly chromicmaterials, and in particular thermoplastic materials comprising polymersand these polychromic substances. The polymers may be polyolefins suchas polyethylene, polyethylene terephthalate, polypropylene, or mixturesthereof.

WO 2012/114121 relates to the reversible activation of certaindiacetylenes. These undergo a topochemical polymerisation reaction togive coloured diacetylenes only when they are simultaneously exposed toadditional activating stimuli. This document discloses that reversibleactivation is advantageous because the compounds have high environmentalstability in coatings or in plastics parts. The diacetylene compoundsare applied to or incorporated within substrates, the substrates arethen exposed to a first activating stimulus which converts thediacetylene compounds from an unreactive form to a reactive form, andsubsequently a second stimulus that causes the reactive form of thediacetylene compound to polymerise and form coloured substrates. Onremoval of the activating stimulus the diacetylene compound reverts toits unreactive form. The substrate may be packaging.

A different type of laser marking is disclosed in WO 2007/141522. Inthis document, a non-stoichiometric compound such as reduced indium tinoxide (r-ITO) functions as a highly effective absorber of near infra-redradiation and is useful in combination with a marking component such asan ammonium octamolybdate based ink formulation. The result is toproduce a colour-forming reaction in respect of a component that wouldotherwise undergo the desired reaction on irradiation at a differentwavelength.

WO 2010/001171 discloses several different types ofdiacetylene-containing compounds and their uses to impart colour tomaterials by subjecting the materials to irradiation. Amongst thepreferred colour-forming diacetylenes mentioned in the document arethose which are capable of forming at least two distinct coloursselected from blue, red, green, cyan, magenta and yellow (particularlypreferably those which change from colourless to blue), and those whichgive rise to electrical conductivity as well as colour onpolymerisation.

WO 2007/045912 is particularly concerned with laser imaging ofsubstrates such as paper, card or board. This document discloses amethod of marking a substrate comprising the steps of coating thesubstrate with a white or colourless solution of a soluable alkali oralkaline earth metal salt of a weak acid, and irradiating areas of thesubstrate to be marked such that those areas change colour.

WO 20006/114594 discloses an example of a printing system and apparatusfor the laser marking of a substrate. The apparatus comprises a laserdiode for emitting a beam of laser light and a galvanometer for aligninga desired point on the substrate with the laser beam such that the laserbeam irradiates the desired point thus causing an additive to changecolour at said point. The document discloses that the system may be usedon a wide variety of substrate materials, for example, metals, alloys,glasses, ceramics, plastics, fabrics, wood, paper, card, resins,rubbers, foams, composites, stone and edibles.

WO 2006/114600 similarly discloses a substrate marking system andapparatus. The emphasis on this document is on multi-colour printing.Additives are used which are susceptible to changing colour to one of atleast two selectable colours upon irradiation, each selectable colourbeing different from the colour of the additive prior to irradiation. Aswell comprising a laser diode for emitting a beam of laser light andmeans for aligning a desired point on the substrate with the laser beam,the apparatus also comprises a means for controlling a fluence level ofthe laser beam to select the resultant colour of the additive from theselectable colours.

WO 92/07297 discloses a laser imagable composition comprising aparticular combination of certain polyacetylenic compounds and certainpolycarbocyanine dyes. The compositions are prepared under atmosphericconditions by forming a dispersion, emulsion or suspension, preferablyan aqueous dispersion in a binder to provide a dispersion containingfrom about 1 to about 50%, preferably from about 4 to about 20% of solidpolyacetylenic microcrystals. The document states that thepolycarbocyanine dyes are effective heat transmitting agents and thatonly small amounts of these dyes are needed to provide desiredabsorptions. They are said to transmit heat in excess of a criticaltemperature of the thermochromic polyacetylenes. The polycarbocyaninedyes disclosed in this document are disadvantageous in terms of theiroptical properties including their colour and transparency. Thisdocument does not disclose inorganic energy absorbers/heat transmitters.

WO 2006/051309 discloses a photothermal recording medium which is acolourless or transparent composition comprising a charge-delocalisationcompound and a photoacid, wherein the photoacid generates an acid onirradiation or heating, thereby forming a coloured charge-transfercomplex with said compound.

WO 2006/113778 is another document which discloses laser activatedthermochromic compositions. The document in particular relates to thinfilms and coatings of such compositions that undergo an irreversiblecolour change when heated by laser energy. The use of a stabiliser inthe form of a radical trap is essential in accordance with thisdocument. Various different types of thermochromic dyes and stabilisersare disclosed.

EP 0 600 441 discloses a laser marking method comprising irradiatinglaser light on a thermosensitive colour forming ink layer formed on asubstrate, the ink layer being formed by printing with a printing inkcomprises a leuco dye as a colour former and an acid substance as acolour developer, in which the printing ink further comprises at leastone background colour formation inhibitor selected from the groupconsisting of a water-soluble amino acid, an ammonium salt of aninorganic acid, a pH buffer, and water.

WO 2007/114829 is a further document which is concerned with lasermarking and in particular relates to a coating composition which can beused in the product and package labeling field. This document disclosesa coating composition comprising electron donor dye precursorparticulars encapsulated with a polymer having a glass transitiontemperature Tg, of from about 150® C. to about 190® C. The documentdiscloses specific electron donor dye precursors as being suitableincluding fluorine and phthalide compounds. The high temperaturesdisclosed in this document are disadvantageous in terms of suitabilitywith various polymeric films some of which can only be handled at lowtemperatures.

WO 2007/057367 discloses tetrabenzodiazadiketoperylene pigments forlaser marking. This produces a florescent marking readily apparent underUV light but not readily apparent under ambient light. The documentstates that this could be useful in for example security marking andbrand identification of printed packaging.

EP 1 852 270 relates to laser marking in the context of laminates. Oneof the layers in the laminate is a transparent thermoplastic resinexhibiting good light transmittance. Another layer comprises athermoplastic polymer composition containing a chromatic colorant and ablack substance in particular ratios. The laminate can be marked in twoor more different colour tones by irradiating with two or more laserlights having different energies from each other.

EP 0 764 548 discloses a thermosensitive recording adhesive label sheetcomprising various components. A layer is included which comprises anelectron donating colouring compound (leuco dye) serving as a colouringagent and an electron accepting compound serving as a colour developer(capable of inducing colour formation in said leuco dye upon applicationof heat thereto). Other components in the product include a support, aprotective layer, an adhesive layer and a disposable backing sheet.

WO 2010/112940 is another document which relates to the use of certaindiacetylenes in laser imaging. This document discloses applyingactivable colour forming compounds to substrates wherein the activablecolour forming compounds are initially unreactive but become reactiveupon activation. The colour forming compound may be activated in theareas of the substrate were the image is to be formed, followed byreacting the activated colour forming compound into its colour form toproduce an image.

WO 2007/003030 discloses acetal copolymers which are thermally reactivenear-infra-red absorbing copolymers. The focus is on the production oflithographic printing plates for computer-to-plate and digital offsetpress technologies, photo resist applications, rapid prototyping ofprinted circuit boards, and chemical sensor development. The copolymermay be used in the preparation of a coating for use in those product.

WO 2006/018640 relates to multi-colour printing using laser marking withpolydiacetylene chemicals. The document states that the polydiacetylenestypically exhibit a colour (or a shade of colour) dependent on thedegree of polymerisation and therefore that by controlling the degree ofpolymerisation of a diacetylene, a variety of colours from blue throughto red and possibly even yellow can be produced. In other words, multicolour printing can be achieved simply and specifically, especially byusing one or more UV lasers. The method in this document comprisesapplying a combination of a diacetylene and a photo acid or photo base,and polymerising the diacetylene by radiation, preferably UV radiation,in order to form an image. Polymerisation may occur to differing degreesin different areas, and the laser may be tuneable.

U.S. Pat. No. 6,376,577 discloses laser-markable plastics whichcomprise, as dopant, graphite particles having one or more coatings.This enables high contrast to be achieved.

U.S. Pat. No. 5,139,926 and U.S. Pat. No. 5,215,869 disclose preparationof a supported modulating film having a permanent yellow imaged layer ofthe homopolymer of 10,12-docosadiyndioc acid monomer.

US 2012/00103045 discloses an intrinsically markable laser pigment inthe form of a reducible metal compound.

GB-A-2352854 discloses laser markable materials comprising athermoplastic elastomeric polymer, pigmented with titanium dioxide.

WO 2010/029276 relates to laser imaging and its use in securityapplications. This discloses a method of forming an invisible indiciumon an article that comprises an outer opaque layer and an inner,laser-imagable layer, which comprises irradiating the article with alaser, whereby the laser radiation passes through the opaque layer, andcauses the laser-imagable layer to change colour. The article can bescanned as a security check. Thus, laser imaging is said to be useful inorder to mark articles with covert indicia in order to preventcounterfeiting, forgeries and ID theft. This is disclosed as potentiallybeing useful with official documents such as passports, identity cards,bank notes, high branded value goods, pharmaceutical compositions,foodstuffs and pin numbers or other access codes.

WO 2005/068207 is a further document relating to the use of functionalIR-absorber/colour developers to enhance laser imaging. For example,certain copper salts are useful in order to bring about a colour-formingreaction that would otherwise occur only at a different wavelength.

WO 20/074548 discloses yet further laser-markable compositions whereinthe ink composition comprises a solvent, a binder (preferably but notessentially having a labile group) and an oxyanion of a multivalentmetal. The metal oxyanion is preferably ammonium octamolybdate.

WO 2006/108745 discloses coating compositions which yield colouredimages of good intensity and durability, which can be modulated in orderto achieve either transparent or opaque coatings. Various differentcompounds are disclosed. The document discloses exposing the parts ofthe coated substrate, where a marking is intended, to energy in order togenerate a colour marking. The energy may for example be infra-redirradiation.

WO 2007/088104 discloses a composition which comprises a latentactivator and a colour former. The latent activator may be an acidderivative or a salt of an acid and an amine. The colour former may beselected from various groups including phthalides, fluorans,trarylmethanes, benzoxazines, quinazolines, spiropyrans, quinones,thiazines and oxazines and mixtures thereof. The substrate may be markedby coating a substrate with the composition and exposing those parts ofthe coated substrates, where a marking is intended, to energy (forexample UV, IR, visible or microwave irradiation) in order to generate amarking.

WO 2011/089447 is another case relating to apparatus and systems usedfor inkless printing. There is a substrate which includes materialsusceptible to change colour upon irradiation, a radiation sourceoperable to produce radiation at two or more distinct wavelengths, andmeans for controlling the emission of radiation from the radiationsource so as to controllably irradiate selected areas of the substratewith desired quantities of radiation from the radiation source so as tomark the substrate in a desired manner.

WO 2008/107345 discloses a laser-sensitive recording material. There isa substrate coated with a recording layer and an undercoating layer. Therecording layer undergoes a colour change on heat treatment produced bylaser irradiation and the undercoating layer comprises a pigment.

WO 2008/050153 relates to a laser markable composition comprising amarking component and an organic compound, wherein the organic compoundabsorbs laser light and causes the marking components to change colour.The organic compound is defined in terms of its absorptivity ratio andvarious possible organic compounds are disclosed.

WO 2007/063339 discloses a laser imagable marking composition comprisinga dye responsive to the presence of hydrogen ions but substantiallynon-responsive to irradiation or heating, a compound that generates anacid on irradiation or heating, and a binder. The acid-generatingcompound may be responsive to irradiation, for example near infra-redradiation or UV irradiation. The document discloses that effectivemarking can be achieved in a variety of colours. The composition isstated as being typically initially colourless or transparent and can beused to mark a substrate or polymer matrix effectively, usingnon-visible radiation.

Yet further examples of diacetylene laser-writable pigments aredisclosed in WO 2010/089595 and WO 2011/121265.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in further non-limitingdetail and with reference to the FIGS. in which:

FIG. 1 is a surface plot showing the effect of laser-writable pigmentparticle size and coating thickness on the gloss of a film which hasbeen laser-treated.

FIG. 2 is a surface plot showing the effect of laser-writable pigmentparticle size and concentration on the gloss of a film which has beenlaser-treated.

FIG. 3 is a surface plot showing the effect of laser-writable pigmentparticle size and concentration on the red reflection 1 values of a filmwhich has been laser-treated.

FIG. 4 is a surface plot showing the effect of laser-writable pigmentparticle size and coating thickness on the red reflection 1 values of afilm which has been laser-treated.

FIG. 5 shows various optical properties as functions of particle size,concentration and thickness.

DETAILED DESCRIPTION

Whilst there have been significant developments in the field of laserwritable substrates over the past few years, improvements are desirablein several areas. Many of the substrates or films on which the laserwriting is carried out are not suitable for certain downstreamprocesses. In addition, many of the existing laser writing technologiesare inefficient in terms of the laser power required to achievesatisfactory results.

One object of the present invention is to enhance the efficiency withwhich desired optical properties can be obtained when laser writing. Afurther object of the present invention is to facilitate theapplicability of laser writability to a wide range of products andprocesses, and in particular so that the films are suitable fordownstream processes in the films field, for example in labels such aspressure sensitive labels.

From a first aspect the present invention provides a compositioncomprising a laser writable pigment wherein at least 50% of the laserwritable pigment particles have a particle size of less than about 1micrometer.

The composition may be transparent prior to laser writing. Thecomposition may also or instead be colourless prior to laser writing.These features tend to make the composition best suited for applicationto filmic materials for use in packaging and labelling applications, andfor security documents such as bank notes, ID cards, passports and thelike.

The film of the invention is not intended for use as a photographicfilm.

By “laser writable” we mean that the laser writable component, or asubstrate incorporating that component, undergoes a non-pyrolyticchemical or molecular identifiable change in at least one observable ormeasurable characteristic on exposure to laser radiation. The observableor measurable characteristic may be, or may include, the appearance ofthe component and/or the substrate in which it is incorporated, whichmay include the visible appearance (e.g. the colour) of the componentand/or the substrate in which it is incorporated. The non-pyrolyticchemical or molecular change may be a chemical, stereochemical oroxidative change, but is not a pyrolytic change and is preferably not adecompositional or substantially decompositional change.

“Identifiable” means discernible by inspection, including visualinspection, or by other measurement or characterisation.

When the composition is incorporated into a substrate, such as a filmicsubstrate or coating therefor, the identifiable change on exposure tolaser radiation effects a corresponding identifiable change in thesubstrate, but preferably without pyrolytically or decompositionallyaffecting the molecular structure of the substrate adjacent thecomponent. In this sense at least the composition of the invention isdistinguished from certain prior art disclosures which teach thecreation of visual or other changes in substrates caused by subjectingthose substrates or components thereof to laser radiation effective tochange the appearance of the substrate by pyrolysis and/or decompositionof molecular components of the substrate. Thus for example a polymericsubstrate incorporating carbon black or inorganic pigment particles inwhich laser bombardment of the particles causes the polymeric moleculesadjacent such particles to heat up and change appearance as a result ofpyrolytic or decompositional change are not “laser writable” in thesense in which that phrase is meant herein. When the composition isincorporated into substrate, the substrate becomes “laser writable” inthe sense meant herein such that the substrate undergoes a non-pyrolyticchemical or molecular identifiable change in at least one observable ormeasurable characteristic on exposure to laser radiation, whereinpreferably there is substantially no destruction of the molecularstructure of the substrate during laser writing.

Other terms such as “laser printable”, “laser imagable” and “lasermarkable” may be used more or less synonymously with “laser writable”.However, “laser printable” in this connection does not mean printable bymeans of using a laser printer. Rather, “laser printable” means that asubstrate incorporating the composition of the invention is printable inthe sense that an identifiable change in the appearance of the substratebecomes apparent upon exposure of the composition within that substrateto laser radiation in the manner described above and with reference tothe definition of “laser writable”.

Thus from a second aspect the present invention provides a compositioncomprising a laser writable pigment wherein at least 50% of the laserwritable pigment particles have a particle size of less than about 1micrometer, and wherein the pigment undergoes a non-pyrolytic chemicalor molecular identifiable change in at least one observable ormeasurable characteristic on exposure to laser radiation.

The laser writability of the pigment, of the composition comprising thepigment or of a substrate incorporating the composition may be such thata single identifiable change may be effected by laser writing, but insome cases more than one identifiable change may be effected.

Consequently, from a third aspect the present invention provides acomposition comprising a laser writable pigment wherein at least 50% ofthe laser writable pigment particles have a particle size of less thanabout 1 micrometer, and wherein the pigment undergoes a firstnon-pyrolytic chemical or molecular identifiable change in at least oneobservable or measurable characteristic on exposure to a first laserradiation and wherein the pigment undergoes a second non-pyrolyticchemical or molecular identifiable change in at least one observable ormeasurable characteristic on exposure to a second laser radiation.

The first and second laser radiation may be the same or different interms of their type, power, frequency and/or duration. For the avoidanceof doubt in this connection the second laser radiation may for examplesimply comprise a prolongation of the first laser radiation, or it mayemanate from an altogether different source.

A simple example of such a change would be a sequential colour change,for example from clear to blue on exposure to a first dose of laserradiation and from blue to red on a second dose of laser radiation.

It has previously been assumed that there is no advantage in usingextremely low particle sizes; in fact, very low particle sizes have beenavoided so as to avoid the need for extensive milling. Furthermore, theskilled person has generally not been motivated to reduce the particlesize because for a given weight of material this results in a largernumber of particles which can make processing more difficult, forexample in terms of viscosity or in binding the material.

It has surprisingly now been found that improved optical properties canbe obtained with lower particle sizes and that processability is stillreasonable and manageable even with such particle sizes. Furthermorelower particle sizes result in more efficient lasing, i.e. less energyinput is required in order to bring about effective laserwriting/marking.

The particle sizes can be expressed in terms of their d₅₀ value, namelythe maximum diameter of 50% of the particles. Preferred d₅₀ valuesinclude less than about 500 nanometers, 400 nanometers, 300 nanometers,200 nanometers or 100 nanometers.

The small particle size of the present invention results in a highgloss, clear product, which has excellent optical properties across abroad gamut of colours.

Without wishing to be bound by theory, it may be the case that, for afixed concentration, a reduction in particle size increases the surfacearea available for light absorption and reflection. Reducing theparticle size seems to bring improvements in a non-linear manner,presumably because with approximately spherical particles the surfacearea increases in a non-linear manner.

Optionally other components present in the composition may also havesmall particle sizes as defined above.

According to the present invention the composition may be a coatingcomposition.

Preferably the coating composition is for coating a polymeric film or abiopolymer film.

Alternatively the composition of the present invention may be a polymerfilm substrate or a biopolymer film substrate itself. In other words thelaser writable pigment may be incorporated into the body of thesubstrate film, rather than being part of a coating composition appliedto it.

In a further alternative, the composition of the present invention maybe a layer on or in a polymer film or biopolymer film.

Preferably the composition of the present invention is used as a coatingor skin layer on a polymer film or biopolymer film. For example thecomposition may be coated, coextruded or melt coated on the substrate.

The use of coatings or skin layers is particularly advantageous sincethis allows the laser writable pigment particles to be concentrated intoparticular thin surface layers thereby enhancing the efficacy with whichlaser writing can be carried out.

The compositions comprising the laser-sensitive pigments are encompassedwithin the present invention both in their “wet” form (i.e. a solutionor suspension containing the pigment and other materials, for example acoating composition solution/suspension) and in their “dry” form (i.e.after removal of the water or other solvent, for example a driedcoating).

From a further aspect the present invention provides a laser writablecoating or layer on a polymeric film or biopolymer film, wherein thethickness of the layer or coating is less than 10 micrometers.

It has surprisingly been found that low thicknesses give excellentoptical properties, particularly in terms of clarity and transparency.Both of these characteristics are important: high clarity means thatimages or indicia can be seen clearly, and high transparency means thatlight transmission is high. Furthermore, the coatings may be formed byprocesses (e.g. reverse gravure coating) which achieve thicknesseswithin a particular percentage variation, and a particular percentagevariation of a thin coating is less than the same percentage variationof a thick coating; therefore there is greater uniformity and lesscolour variation. Another advantage is that thin coatings are lessexpensive than thick coatings.

Preferred thicknesses include less than 5 micrometers, less than 4micrometers and less than 3 micrometers.

The thickness may be about 20 microns or less, or about 15 microns orless.

The coating may be applied to the film by any appropriate method asknown in the art, for example by reverse gravure printing.

From a further aspect the present invention provides a composition(optionally a coating or layer in or on a polymer film) comprising alaser writable pigment in a concentration of 25 to 50% by weight of thetotal composition when dry.

It has been found that concentrations within this range bring aboutexcellent optical properties. Preferred concentration ranges include 30to 45% by weight and 35 to 40% by weight or the total composition whendry.

From a further aspect, the present invention provides a film comprisinga laser writable composition (optionally as coating or layer in or onthe film substrate) wherein the film has a gloss of greater than 70gloss units (GU).

“Gloss” as referred to herein is surface or specular gloss being theratio of the luminous flux reflected from, to that incident on, thesample being measured for specified solid angles at the speculardirection i.e. the angles of incidence and reflection are equal. Glossvalues referred to herein are gloss (45°) values, i.e. the angle used is45°. The test method is described in ASTM D2457. The measurement ofsurface gloss of films may be made using a Novo gloss glossmeter with arho point of 45°.

The high gloss products of the present invention are particularlyadvantageous in terms of appearance and applicability in a variety ofproducts and application. High gloss products are aesthetically andcommercially desirable. They result in high definition images, text andother visual characteristics rather than diffuse appearance. In somecases glossy materials are advantageous in giving a “no look” label forexample in the beer and beverage industry.

Preferred gloss values include greater than 80% or greater than 85 glossunits, in some cases greater than 95 or higher.

One particular advantage of the present invention is that thecoefficient of friction can be tuned.

From a further aspect the present invention provides a film comprisingor carrying a laser writable composition (optionally as a coating orlayer in or on the film) wherein the product has a coefficient offriction of between 0.2 and 2.

The present invention is suitable for use with products which can have arange of friction properties. The friction characteristics can becontrolled or tuned independently with respect to the printed appearancebecause the laser writing/printing/marking in most cases does not affectthe friction characteristics.

The coefficient of friction of the products of the present invention isparticularly advantageous in downstream handling of the products. It canmean that the products can be processed and handled well and stacked andunstacked in a convenient manner.

In some applications (for example in some packaging such as that usedfor wrapping (e.g. twist wrap), high friction is required so that theproduct can stick to itself or be held against itself easily. In otherapplications (for example where high speed processing through apparatusis the main factor) low friction is desirable. In yet other applications(for example where product needs to be produced relatively quickly butwhere stacking is required) a balance is desirable. In one example thehigh speed packing of reams of paper requires appropriate frictioncharacteristics. In another example the use of reels means that thefriction characteristics of the wound product must be high enough toavoid problems such as telescoping. A further consideration is that thematerial should not have such high friction characteristics so as toresult in static problems.

The coefficient of friction referred to herein is preferably the dynamiccoefficient of friction. Suitable coefficient of friction values caninclude about 0.4 to 0.9, 0.2 to 0.6, 0.2 to 1, 0.2 to 0.4 or 0.3 to0.5, for example, depending on the application.

The coefficient of friction values referred to herein are preferably inrespect of the product to itself.

From a further aspect the present invention provides a film comprisingor carrying a laser writable composition (optionally as a coating orlayer in or on the film) wherein the product has a clarity of greaterthan 95%.

Preferred clarity values include greater than 96%, preferably greaterthan 97%.

From a further aspect of the present invention provides a filmcomprising or carrying a laser writable composition (optionally as acoating or layer in or on the film) wherein the product has a haze ofless than 15%.

Preferred haze values include less than 5%, or less than 3%.

Haze referred to herein is the wide angle haze (WAH) of a film—thepercentage of transmitted light which is passed through the film whichdeviates from the incident beam by more than 2.5 degrees of forwardscattering. Measurements of WAH of films may be made using an E.ELSpherical Haze Meter. The test method is described in ASTM D1003.

Additionally or alternatively, product may have a narrow angle hazevalue of about 3.0%) or lower, about 2.5% or lower, about 2.0% or lower,about 1.5% or lower, or about 1% or lower.

The narrow angle haze (NAH) of a film is the amount of parallel lightwhich is scattered by more than 6 minutes (0.1°) of arc when passingthrough the film sample from the incident beam. NAH is measured as apercentage of the total light transmitted through the film. Themeasurement of NAH of films may be made using laser narrow angle hazemachines.

Thus the high clarity values referred to herein are the converse of thelow narrow angle scattering values. High clarity correlates tosee-through quality, i.e. how well fine details can be seen through thespecimen.

From a further aspect the present invention provides a film which isboth laser writable/printable/markable and ink printable. This may be byvirtue of the properties of a coating or layer in or on the film or ofproperties of the film bulk substrate itself.

Considerable further flexibility, functionality and advantages can beprovided when laser writability and conventional printability arecombined. By “ink printable” is meant any conventional or known printingtechnique including for example water based, solvent based or UV basedtechnologies, and including for example flexographic (flexo), gravure,screen printing and rotary screen printing methods. UV flexo ispreferred.

The substrates of the present invention are suitable for a wide varietyof printing processes. For example label face stock—optionally forpressure sensitive adhesive labels—can be used for both conventionalprinting options and also laser writing.

One example of why the combination of laser writing and conventionalprinting is useful is as follows. In some industries, for example infast moving consumer goods (FMCG) industries, large quantities of thesame or similar product, packaging or label are used. Most of theinformation is the same on each item (e.g. the brand, the bulk of thedesign, various information, etc.) and therefore is suitably imparted byconventional printing methods which are cost-effective for large printruns (for example UV Flexo). Often, a smaller amount of additionalinformation is useful on smaller batches, e.g. to provide country- ormarket-specific tailoring, to promote special offers, to provideindications as to when the item was made or filled or when it should beconsumed or used by (e.g. “best before” or “use by” dates), or for anyother purpose where tailoring or modification of the visual appearanceor indicia is desired. Laser writing/marking/printing is ideally suitedto such uses with respect to smaller runs or even individual items,whereas conventional printing is not cost-effective with such smallscale or low volume work. In other words, laser writing/printing/markingand conventional printing can be used in combination such that each isused cost-effectively.

Various characteristics are referred to herein and the skilled personwill understand at which stage in the process the characteristics areimportant. For example, desired gloss, clarity, haze and other opticalproperties such as a broad colour gamut are important in the finalproduct, but optionally may also be desirable after partial printing inthe event that the product may be used or is intended to be used aftersuch partial printing. The friction characteristics are optionallyimportant at the stage at which the product is handled or processed ormay be processed downstream. In the case of films and other substratesthe properties may optionally be applicable to the product including thefilm, not just the laser-writable coating or skin layer.

The laser writable pigment may be any known laser writable pigment,including those disclosed in the prior art summarised above. Theinvention works particularly well with laser writable organic pigments,for example those with sp or sp2 hybridized carbon atoms, for examplethose with ethylenic or acetylenic unsaturation. Diacetylene basedpigments, for example such as those disclosed in the prior art documentssummarised above may be particularly mentioned. A wide range of suchpigments is available including full colour laser writable pigments. Forexample, the laser writable diacetylene-based pigments may be selectedfrom those disclosed in any of WO 2009/093028, WO 2009/081385, WO2012/114121, WO 2010/001171, WO 2010/112940, WO 2006/018640, WO2010/089595 and WO 2011/121265.

As known in the art, the diacetylene-containing materials may befunctionalised into amide form. The diacetylene-containing compound maybe based on 10,12-docosadiyndioic acid, for example an amide derivativethereof, e.g. 10,12-docosadiyn-bis-propargylamide, as disclosed in WO2010/112940.

The laser markable pigment may be a material which allows a change fromcolourless to monochrome (e.g. clear to black) or degrees thereof. Forexample the colour changer may be Pergascript Black 1C (BASF) or arelated product.

By laser writable pigment, or laser markable/printable/imagable pigment,can be meant any of the compounds known which can undergo a change inappearance on laser irradiation. The change in appearance may be forexample a change from invisible to visible appearance, a change from onevisible appearance to another visible appearance, a colour change, achange in extent or hue of colour, a monochrome change, or anycombination of these.

In accordance with the present invention, optionally the irradiationdoes not need to be laser irradiation. For example, as is known in theart, other sources of energy including other lamp, diode and otheremission arrangements are possible. Nevertheless, where accurate, sharpor focussed printing is required, laser radiation is preferred.

In accordance with the present invention, the change of appearance maybe brought about by various forms of energy, such as IR, visible or UVradiation. For example, as is known in the art, UV radiation may bringabout one change, heat may bring about a different change, and infraredor near-infrared radiation may bring about a different change. Many ofthe known compositions are appropriate for use with, and are indeeddesigned for use with, a sequence of energy exposure, particularly if arange of colours or appearances is required. For example, diacetylenesare well known to undergo a sequence of changes, e.g. an initial changeon exposure to UV energy, and subsequent changes when heated, so thatthey can be used to produce various colours. These properties originatefrom the chemical structure and reactivities of the diacetylenesincluding their ability to polymerize, and are known to the skilledperson. In accordance with the present invention the skilled person willunderstand that diacetylene compounds are not essential but that otherlaser writable pigments which undergo one or more changes as known inthe art may alternatively or additionally be used.

More than one laser writable pigment may be used, or a combination oflaser writable pigment(s) and other pigments or colour/appearance changeagents may be used.

Optionally, additives may be used in the present invention in order toenhance the efficacy of the process, as known in the art.

For example, energy absorbers such as e.g. infrared or near infra red(NIR) absorbers can be incorporated to enhance the process. Suitable IRabsorbers include indium tin oxide (ITO) for example or otheringredients known for this purpose, as for example disclosed in theprior art described above.

Preferably the composition includes a diacetylene and an NIR absorber.

Alternatively the energy absorber may be SABoTBA(Tri-n-butylammoniumborodisalicylate). Optionally this may be used incombination with the pigment changer Pergascript Black 1C.

A further advantage of the present invention is that it is possible tobring about a large colour gamut thereby enhancing the opticalproperties of the film. Previously it has not been possible to obtainsuch a good surface finish together with the colour gamut and optionallythe downstream surface characteristics desired.

Other optional components may be present in the composition as required,including conventional additives and components known in the art.

For example, components of coating compositions including binders andother ingredients are well known in the art.

In a further aspect the present invention comprises a product where thefilm is one component part.

From a further aspect the present invention provides a label, forexample a pressure sensitive adhesive label, comprising the film of thepresent invention.

From a further aspect the present invention provides a packaged productwherein the film of the invention is used in the packaging.

The use of the film in a packaging context may, for example, include itsuse as a container, sleeve, lid, label or wrapper. The film may be usedon its own or may be combined with other materials, for example as partof a laminated structure.

The films used in the present invention, prior to deposition of anycoating and/or skin or lamination layer may comprise any suitablepolymeric filmic substrate, such as films made from biopolymers [e.g.polylactic and/or cellulosic films (e.g. microbial and/or regeneratedcellulose film)]; thermoplastic films; polymeric films (for examplefilms comprising: polyolefins [e.g. polypropylene and/or polyethylene]polyurethanes, polyvinylhalides [e.g. PVC], polyesters [e.g.polyethylene terephthalate-PET], polyamides [e.g. nylons] and/ornon-hydrocarbon polymers); and/or multilayer and/or composite sheetsformed by any suitable combinations and/or mixtures of thereof. Suitablefilmic substrates therefore include polyolefinic films, but alsopolyester films, polyurethane films, cellulosic and PLA films.

The film may therefore comprise a cellulosic material, polymericmaterial and/or thermoplastic polymer, and may conveniently comprisepolymers of low surface energy. More preferably the sheet comprises ahomopolymer, a crystalline polymer and/or a polymer of randomly orientedamorphous non-crystalline polymer chains. Most preferably the sheetcomprises: polyolefins [e.g. polypropylene and/or polyethylene]polyurethanes, polyvinylhalides [e.g. polyvinyl chloride (PVC)],polyesters [e.g. polyethylene terephthalate-PET], polyamides [e.g.nylons] and/or non-hydrocarbon polymers).

Conveniently the polyolefin films to be used with the present inventionmay comprise one or more polyolefins [e.g. polypropylene homopolymer,polyethylene homopolymer (e.g. linear low-density polyethylene-LLDPE)and/or polypropylene/polyethylene copolymer(s); optionally in one ormore layers]. The constituent polymers and/or layers in a film of thepresent invention may be oriented, blown, shrunk, stretched, cast,extruded, co-extruded and/or comprise any suitable mixtures and/orcombinations thereof. Preferred films comprise a major proportion ofpolypropylene and/or an olefin block copolymer containing up to about15% w/w of the copolymer of at least one copolymerisable olefin (such asethylene). More preferred films comprise polypropylene homopolymer, mostpreferably isotactic polypropylene homopolymer.

Films may optionally be cross-linked by any suitable means such aselectron beam (EB) or UV cross-linking, if necessary by use of suitableadditives in the film.

The definition of polyolefin, as intended herein, is a polymer assembledfrom a significant percentage, preferably ≧50% by weight of one or moreolefinic monomers.

The definition of copolymer herein is a polymer assembled from two ormore monomers. Such polymers may include, but are not limited to,polyethylene homopolymers, ethylene-α-olefin copolymers,polypropylene-α-olefin copolymers, polypropylene homopolymers,ethylene-vinyl acetate copolymers, ethylene-methacrylic acid copolymersand their salts, ethylene-styrene polymers and/or blends of suchpolymers. The polymers may be produced by any suitable means, forexample one or more of free radical polymerisation (e.g. peroxycompounds), metallocene catalysis and/or coordination catalysis (e.g.Ziegler and/or Natta catalysts and/or any variations thereof).

Polymeric resins used to produce the films of the present invention aregenerally commercially available in pellet form and may be melt blendedor mechanically mixed by well-known methods known in the art, usingcommercially available equipment including tumblers, mixers and/orblenders. The resins may have other additional resins blended therewithalong with well-known additives such as processing aids and/orcolorants. Methods for producing polyolefin films are well-known andinclude the techniques of casting films as thin sheets through narrowslit dies, and blown-film techniques wherein an extruded tube of moltenpolymer is inflated to the desired bubble diameter and/or filmthickness.

For example to produce a polymeric film the resins and additives may beintroduced into an extruder where the resins are melt plastified byheating and then transferred to an extrusion die for formation into afilm tube. Extrusion and die temperatures will generally depend upon theparticular resin being processed and suitable temperature ranges aregenerally known in the art or provided in technical bulletins madeavailable by resin manufacturers. Processing temperatures may varydepending upon process parameters chosen.

Thus, the polymeric film can be made by any process known in the art,including, but not limited to, cast sheet, cast film, or blown film.This invention may be particularly applicable to films comprisingcavitated or non-cavitated polypropylene films, with a block copolymerpolypropylene/polyethylene core and skin layers with a thicknesssubstantially below that of the core layer and formed for example fromrandom co-polymers of ethylene and propylene or random terpolymers ofpropylene, ethylene and butylene. The film may comprise a biaxiallyorientated polypropylene (BOPP) film, which may be prepared as balancedfilms using substantially equal machine direction and transversedirection stretch ratios, or can be unbalanced, where the film issignificantly more orientated in one direction (MD or TD). Sequentialstretching can be used, in which heated rollers effect stretching of thefilm in the machine direction and a stenter oven is thereafter used toeffect stretching in the transverse direction. Alternatively,simultaneous stretching, for example, using the so-called bubbleprocess, or simultaneous draw stenter stretching may be used.

A film of the present invention may be oriented by stretching at atemperature above the glass transition temperature (Tg) of itsconstituent polymer(s). The resultant oriented film may exhibit greatlyimproved tensile and stiffness properties.

Conveniently a film comprising a propylene homopolymer is oriented at atemperature within a range of from about 145° C. to 165° C. Orientationmay be along one axis if the film is stretched in only one direction, ormay be biaxial if the film is stretched in each of two mutuallyperpendicular directions in the plane of the film. A biaxial orientedfilm may be balanced or unbalanced, where an unbalanced film has ahigher degree of orientation in a preferred direction, usually thetransverse direction. Conventionally the longitudinal direction (LD) isthe direction in which the film passes through the machine (also knownas the machine direction or MD) and the transverse direction (TD) isperpendicular to MD. Preferred films are oriented in both MD and TD.Orientation of the film may be achieved by any suitable technique. Forexample in the bubble process the polypropylene film is extruded in theform of a composite tube which is subsequently quenched, reheated, andthen expanded by internal gas pressure to orient in the TD, andwithdrawn, at a rate greater than that at which it is extruded, tostretch and orient it in the MD. Alternatively a flat film may beoriented by simultaneous or sequential stretching in each of twomutually perpendicular directions by means of a stenter, or by acombination of draw rolls and a stenter. A preferred oriented filmcomprises biaxially oriented polypropylene (known herein as BOPP), morepreferably the BOPP film described in EP 0202812.

The degree to which the film substrate is stretched depends to someextent on the ultimate use for which the film is intended, but for apolypropylene film satisfactory tensile and other properties aregenerally developed when the film is stretched to between three and ten,preferably, seven or eight, times its original dimensions in each of TDand MD.

After stretching, the polymeric film substrate is normally heat-set,while restrained against shrinkage or even maintained at constantdimensions, at a temperature above the Tg of the polymer and below itsmelting point. The optimum heat-setting temperature can readily beestablished by simple experimentation. Conveniently a polypropylene filmis heat-set at temperatures in the range from about 100° C. to about160° C. Heat-setting may be effected by conventional techniques forexample by means one or more of the following: a stenter system; one ormore heated rollers (e.g. as described in GB 1124886) and/or aconstrained heat treatment (e.g. as described in EP 023776).

The film may comprise a major proportion of polypropylene such asisotactic polypropylene homopolymer, but also may comprise coextrudedmultilayer films where the polymer of at least one layer is isotacticpolypropylene homopolymer, and the polymer of one or both outer layersis a surface layer polymer having different properties to the isotacticpolypropylene homopolymer.

The sheet of the present invention may consist of only one layer, or thesheet may be multi-layered i.e. comprise a plurality of layers. Thelayers can be combined by lamination or co-extrusion. Preferably thesheet comprises at least three layers where at least one layer(s) aresandwiched between other layers such that none of such sandwichedlayer(s) form either surface of the sheet.

A film of the invention may also be made by lamination of two coextrudedfilms.

One or more layers of the film may be opaque or transparent depending onthe end use of the film. Such layers may also comprise voids introducedby stretch orienting such a layer containing spherical particles of amaterial higher melting than and immiscible with the layer material(e.g. if the layer comprises isotactic polypropylene homopolymer, thensuch particles may be, polybutylene terephthalate, as shown, forexample, in U.S. Pat. No. 4,632,869 and U.S. Pat. No. 4,720,716).Preferably though the film is transparent, making it most suitable forpackaging and labelling applications, and for security documents such asbank notes, ID cards, passports and the like.

Multiple-layer films of the invention may be prepared in a range ofthicknesses governed primarily by the ultimate application for which aparticular film is to be employed. For general use films, having a meanthickness from about 10 μm to about 500 μm, preferably from about 15 μmto about 400 μm are suitable. For certain applications, such aspackaging, preferred films have a mean thickness of from about 25 μm to360 μm, most preferably from about 50 μm to about 350 μm.

If desired, before coating a sheet of the present invention (e.g. with alaser writable coating of the present invention and/or any other coatingand/or layer) it may be subjected to a chemical or physicalsurface-modifying treatment to ensure that the coating and/or layer willbetter adhere to the sheet thereby reducing the possibility of thecoating peeling or being stripped from the sheet. Known prior arttechniques for surface pre-treatment prior to coating comprise, forexample: film chlorination, i.e., exposure of the film to gaseouschlorine; treatment with oxidising agents such as chromic acid, hot airor steam treatment; flame treatment and the like. A preferred treatment,because of its simplicity and effectiveness, is the so-called electronictreatment in which the sheet is passed between a pair of spacedelectrodes to expose the sheet surface to a high voltage electricalstress accompanied by corona discharge.

Optionally if even adhesion of the coating is desired an intermediatecontinuous coating of a primer medium and/or anchor coating can beapplied to a sheet surface treated by any of the methods describedherein. Primer materials may comprise titanates and poly (ethyleneimine) and may be applied as conventional solution coatings [such aspoly (ethylene imine) applied as either an aqueous or organic solventsolution, e.g. in ethanol comprising about 0.5 wt. % of the imine].Another primer medium comprises the interpolymerised condensationacrylic resins prepared in the presence of a C₁₋₆alkanol as described ineither: GB 1134876 (condensing aminoaldehyde with an interpolymer ofacrylamide or methacrylamide with at least one other unsaturatedmonomer); or in GB 1174328 (condensing aminoaldehyde with acrylamide ormethacrylamide, and subsequently interpolymerising the condensationproduct with at least one other unsaturated monomer).

The film may comprise one or more additive materials. Additives maycomprise: dyes; pigments, colorants; metallised and/or pseudo metallisedcoatings (e.g. aluminium); lubricants, anti-oxidants, surface-activeagents, stiffening aids, gloss-improvers, prodegradants, UV attenuatingmaterials (e.g. UV light stabilisers); sealability additives;tackifiers, anti-blocking agents, additives to improve ink adhesionand/or printability, cross-linking agents (such as melamine formaldehyderesin); adhesive layer (e.g. a pressure sensitive adhesive); and/or anadhesive release layer (e.g. for use as the backing material in the peelplate method for making labels).

Further additives comprise those to reduce coefficient of friction (COF)such as a terpolymer described in U.S. Pat. No. 3,753,769 whichcomprises from about 2% to about 15% w/w of acrylic or methacrylic acid,from about 10% to about 80% w/w of methyl or ethyl acrylate, and fromabout 10% to about 80% w/w of methyl methacrylate, together withcolloidal silica and carnauba wax.

Still further additives comprise slip aids such as hot slip aids or coldslip aids which improve the ability of a film to satisfactorily slideacross surfaces at about room temperature for example micro-crystallinewax. Preferably the wax is present in the coating in an amount fromabout 0.5% to about 5.0% w/w, more preferably from about 1.5% to about2.5% w/w. The wax particles may have an average size conveniently fromabout 0.1 μm to 0.6 μm, more conveniently from about 0.12 μm to about0.30 μm.

Yet further additives comprise conventional inert particulate additives,preferably having an average particle size of from about 0.2 μm to about4.5 μm, more preferably from about 0.7 μm to about 3.0 μm. The amount ofadditive, preferably spherical, incorporated into the or each layer isdesirably in excess of about 0.05%, preferably from about 0.1% to about0.5%, for example, about 0.15%, by weight. Suitable inert particulateadditives may comprise an inorganic or an organic additive, or a mixtureof two or more such additives.

Suitable particulate inorganic additives include inorganic fillers suchas talc, and particularly metal or metalloid oxides, such as alumina andsilica. Solid glass or ceramic micro-beads or micro-spheres may also beemployed. A suitable organic additive comprises particles, preferablyspherical, of an acrylic and/or methacrylic resin comprising a polymeror copolymer of acrylic acid and/or methacrylic acid. Such resins may becross-linked, for example by the inclusion therein of a cross-linkingagent, such as a methylated melamine formaldehyde resin. Promotion ofcross-linking may be assisted by the provision of appropriate functionalgroupings, such as hydroxy, carboxy and amido groupings, in the acrylicand/or methacrylic polymer.

Yet still further additives comprise fumed silica for the purpose offurther reducing the tack of a coating at room temperature. The fumedsilica is composed of particles which are agglomerations of smallerparticles and which have an average particle size of, for example, fromabout 2 μm to about 9 μm, preferably from about 3 μm to about 5 μm, andis present in a coating in an amount, for example, from about 0.1% toabout 2.0% by weight, preferably about 0.2% to about 0.4% by weight.

Some or all of the desired additives listed above may be added togetheras a composition to coat the sheet of the present invention and/or forma new layer which may itself be coated (i.e. form one of the innerlayers of a final multi-layered sheet) and/or may form the outer orsurface layer of the sheet. Alternatively some or all of the precedingadditives may be added separately and/or incorporated directly into thebulk of the sheet optionally during and/or prior to the sheet formation(e.g. incorporated as part of the original polymer composition by anysuitable means for example compounding, blending and/or injection) andthus may or may not form layers or coatings as such. These conventionalother coatings and/or layers may thus be provided on top of orunderneath the laser writable coatings of the present invention and maybe in direct contact thereto or be separated by one or more otherintermediate layers and/or coats.

Such additives may be added to the polymer resin before the film ismade, or may be applied to the made film as a coating or other layer. Ifthe additive is added to the resin, the mixing of the additives into theresin is done by mixing it into molten polymer by commonly usedtechniques such as roll-milling, mixing in a Banbury type mixer, ormixing in an extruder barrel and the like. The mixing time can beshortened by mixing the additives with unheated polymer particles so asto achieve substantially even distribution of the agent in the mass ofpolymer, thereby reducing the amount of time needed for intensive mixingat molten temperature. The most preferred method is to compound theadditives with resin in a twin-screw extruder to form concentrates whichare then blended with the resins of the film structure immediately priorto extrusion.

Formation of a film of the invention (optionally oriented and optionallyheat-set as described herein) which comprises one or more additionallayers and/or coatings is conveniently effected by any of the laminatingor coating techniques well known to those skilled in the art.

For example a layer or coating can be applied to another base layer by acoextrusion technique in which the polymeric components of each of thelayers are coextruded into intimate contact while each is still molten.Preferably, the coextrusion is effected from a multi-channel annular diesuch that the molten polymeric components constituting the respectiveindividual layers of the multi-layer film merge at their boundarieswithin the die to form a single composite structure which is thenextruded from a common die orifice in the form of a tubular extrudate.

A film of the invention may also be coated with one or more of theadditives described herein using conventional coating techniques from asolution or dispersion of the additive in a suitable solvent ordispersant. An aqueous latex, (for example prepared by polymerisingpolymer precursors of a polymeric additive) in an aqueous emulsion inthe presence of an appropriate emulsifying agent is a preferred mediumfrom which a polymeric additive or coating may be applied.

Coatings and/or layers may be applied to either or both surfaces of thesheet. The or each coating and/or layer may be applied sequentially,simultaneously and/or subsequently to any or all other coatings and/orlayers. If a laser writable coating of the present invention is appliedto only one side of the sheet (which is preferred) other coatings and/orlayers may be applied either to the same side of the sheet and/or on thereverse (other) side of the sheet.

A coating composition may be applied to the treated surface of sheet(such as the polymer film) in any suitable manner such as by gravureprinting, roll coating, rod coating, dipping, spraying and/or using acoating bar. Solvents, diluents and adjuvants may also be used in theseprocesses as desired. The excess liquid (e.g. aqueous solution) can beremoved by any suitable means such as squeeze rolls, doctor knivesand/or air knives. The coating composition will ordinarily be applied insuch an amount that there will be deposited following drying, a smooth,evenly distributed layer having a thickness of from about 0.02 to about10 μm, preferably from about 1 to about 5 μm. In general, the thicknessof the applied coating is such that it is sufficient to impart thedesired characteristics to the substrate sheet. Once applied to thesheet a coating may be subsequently dried by hot air, radiant heat or byany other suitable means to provide a sheet of the present inventionwith the properties desired (such as an optionally clear; optionallysubstantially water insoluble; highly oxygen impermeable coated filmuseful, for example in the fields of authentication, packaging,labelling and/or graphic art).

It would also be possible to use combinations of more than one of theabove methods of applying additives and/or components thereof to a film.For example one or more additives may be incorporated into the resinprior to making the film and the one or more other additives may becoated onto the film surface.

In a multi-layer film in accordance with the invention having at least asubstrate layer and a skin layer, the skin layer may be preferably inkprintable. The skin layer has a thickness of from about 0.05 μm to about2 μm, preferably from about 0.1 μm to about 1.5 μm, more preferably fromabout 0.2 μm to about 1.25 μm, most preferably from about 0.3 μm toabout 0.9 μm.

The present invention can be used to make various different kinds offilms including clear, white and cavitated films. Clear films arepreferred, as mentioned herein.

From a further aspect the present invention provides a method ofmanufacturing a laser writable film comprising: incorporating within thefilm or a skin layer thereof, or coating the film with a coatingcomprising, a laser writable pigment and optionally other componentssuch as for example an energy absorber as referred to herein.

From a yet further aspect the present invention provides the use of alaser writable film of the present invention for providing an image,information or other visual characteristic(s) on an item, for example inpackaging or labeling.

From a yet further aspect the present invention provides apparatus forpreparing or processing the laser writable composition of the presentinvention.

It will be appreciated that the invention has been described herein interms of various features, for example particle size, thickness,concentration, gloss, friction, clarity, haze, combination printing,type of laser-markable compound, type of energy absorber, type ofcomposition (e.g. coating, skin layer or bulk substrate), method ofpreparation, nature of application, type of use and multicomponentpossibilities, amongst others. Each of the features described herein iswhere appropriate generally applicable and combinable with otherfeature(s) described herein. Thus for example the low particle sizefeature may be combined with any other feature(s) e.g. the combinationprinting feature. In another example the high gloss feature may becombined with any other feature. These are non-limiting examples ofsuitable combinations and the skilled person will understand that anyother appropriate combinations are envisaged.

The present invention will-be described in further non-limiting detailin FIGS. 1-7.

Examples

Coating compositions comprising diacetylide laser-writable pigments(10,12-docosadiyn-bis-propargylamide) were prepared. C50 polypropylenefilm samples available from Innovia Films Limited, Wigton, UK, werecoated with the coating compositions using a Meyer bar or K-bar. Thecoated products were irradiated.

As described below, the particle size of the laser-writable pigment, theconcentration of the laser-writable pigment and the thickness of thecoating were each varied, and the effects on each of gloss, haze,clarity, transmission, static coefficient of friction, dynamiccoefficient of friction, and Lab values were observed.

Methodology for Analyzing the Effect of the Variables on theCharacteristics of the Product

A central composite design was used to show the effect of the threevariables (particle size of the laser-writable pigment, concentration ofthe laser-writable pigment and thickness of the coating) on specificresponses (gloss, haze, clarity, transmission, static coefficient offriction, dynamic coefficient of friction, and Lab values). It was alsoused to optimise the variables for colour gamut and optical properties.

Central composite designs pertain to the estimation (fitting) ofresponse surfaces, following the general model equation:

y=b ₀ +b ₁ *x ₁ + . . . +b _(k) *x _(k) +b ₁₂ *x ₁ *x ₂ +b ₁₃ *x ₁ *x₃ + . . . +b _(k-1,k) *x _(k-1) *x _(k) +b ₁₁ *x ₁ ² + . . . +b _(kk) *x_(k) ²

thereby fitting a model to the observed values of the dependent variabley, that include

(1) main effects for factors x₁, . . . , x_(k),

(2) their interactions (x₁*x₂, x₁*x₃, . . . , x_(k-1)*x_(k)), and

(3) their quadratic components (x₁**2, . . . , x_(k)**2).

In these experiments a rotatable design was used. Each factor (particlesize, concentration and coating thickness) is independent, which is aprerequisite for orthogonality and rotatability.

Coating Formulation

The basic formulation of the coating was made in three steps:

1. A premix or grind was made and then ground to a D95 of 40 microns,

2. The premix was then ground again so that the D50 was the desired sizefor the experimental design.

3. The let-down stage controlled the concentration of the pigment in thecoating, as per the experimental design.

Particle size was measured using a Coulter Counter.

PREMIX TO PRODUCE MILL BASE % by % dry Supplier, Raw Material weightweight Generic name Comments Water 19.66 Joncryl 37.42 23.36 DilutableAcrylic BASF LMV 7085 (34.96% in water) Dispelair 0.24 0.43 Wettingagent Blackburn CF49 Chemicals Ltd, Blackburn, UK Dispex A40 0.42 0.75Anti foam BASF r-ITO 6.04 10.78 Indium tin oxide Evonic (used as an IRabsorber - gives out heat on exposure to IR) 10,12- 36.22 64.88Di-acetylide docosadiyn- pigment bis- propargylamide

The mill base produced from the above-mentioned pre-mix was then mixedwith further ingredients in a let down stage. Five differentcompositions were prepared, with varying concentrations of mill base asshown in the table below.

LET DOWN Generic Supplier, % dry % dry % dry % dry % dry name Commentsweight weight weight weight weight Water Water Mill base Mill Base70.000 60.000 50.000 43.18 76.82 (i.e. the product of the premix)Tinuvin UV BASF 0.790 1.053 1.317 1.496 0.610 1130 stabiliser Tinuvin292 UV absorber BASF 0.520 0.693 0.867 0.985 0.402 CX100 Aziridine DSMNeoResins, 0.150 0.200 0.250 0.284 0.116 Waalwijk Joncryl 8052 AcrylicBASF 28.540 38.053 47.567 54.053 22.054 emulsion

EXPERIMENTAL DESIGN

TABLE 1 Concentration Concentration Actual (% by weight) (% dry weight)Thickness thickness Sam- Size/ of the mill base of the pigment (codedmicrons ple nm in the let down in the dry coating units) (dry) 1 17750.00 32.4 3.00 4 2 413 50.00 32.4 3.00 4 3 177 70.00 45.4 3.00 4.03 4413 70.00 45.4 3.00 4.04 5 177 50.00 32.4 5.00 13 6 413 50.00 32.4 5.0013 7 177 70.00 45.4 5.00 13.02 8 413 70.00 45.4 5.00 13.04 9 96 60.0038.9 4.00 7.7 10 494 60.00 38.9 4.00 7.7 11 295 43.18 28.0 4.00 7.7 12295 76.82 49.8 4.00 7.79 13 295 60.00 38.9 2.32 2.55 14 295 60.00 38.95.68 16.8 15 295 60.00 38.9 4.00 7.7 16 295 60.00 38.9 4.00 7.7 17 29560.00 38.9 4.00 7.7 18 295 60.00 38.9 4.00 7.69 19 295 60.00 38.9 4.007.69 20 295 60.00 38.9 4.00 7.69

Results were Measured in Respect of:

Gloss, Haze, Clarity, Transmission, Coefficient of friction (static anddynamic), and 1 a b values for both the red colouration and the bluecolouration both in transmission (trans) and in reflectance(ref).

The CIE L*a*b* or CIELAB colour scale system was used. The colour spaceis device independent. A HunterLab colour measurement instrument may beused. Lab values relate to the lightness/darkness of the colour (1value) the red green hue (a value) and the blue yellow hue (b value).−100 to + 100 on both a or b values will give the full colour range and0 to 100 on the 1 value will give all chroma options.

The results are shown in Table 2.

TABLE 2 COF COF red red red blue blue blue Sample Gloss TransmissionHaze Clarity Sta Dyn trans l trans a trans b trans l trans a trans b 182.73 93.3 7.56 97.6 1.0110 0.6448 82.95 27.58 −3.98 83.31 −8.02 −15.032 81.67 93.8 6.12 97.4 0.5082 0.5222 83.98 24.76 −3.99 84.35 −7.83−14.30 3 83.50 92.9 8.32 97.4 0.5936 0.5647 81.13 26.29 −4.23 79.61−9.22 −18.62 4 79.30 93.2 7.86 97.6 0.5128 0.485  79.35 32.79 −3.3473.02 −9.89 −26.32 5 86.23 88.3 18.5 97.2 0.6492 0.6196 67.55 53.25−2.62 67.41 −13.35 −29.66 6 74.93 89.8 13.4 97.2 0.5736 0.5508 69.7851.24 −3.47 71.40 −13.24 −26.07 7 73.60 87.2 20.8 97.4 0.5512 0.554762.82 56.43 0.53 64.08 −12.16 −31.00 8 78.63 89.2 12.9 97.2 0.56050.5281 62.18 57.85 0.79 62.19 −11.74 −33.12 9 87.27 89.2 7.86 97.10.6686 0.6261 68.98 51.95 −2.31 69.39 −13.23 −27.38 10 73.93 90.6 13.897.3 0.5683 0.5393 68.02 53.47 −3.57 68.94 −13.27 −28.71 11 81.33 90.411 97.5 1.0140 0.8104 72.28 48.49 −4.74 72.32 −13.14 −26.04 12 78.0789.2 11.7 97.4 0.6925 0.5758 64.32 54.57 −0.81 60.01 −10.10 −35.16 1382.53 93.6 6.13 97.7 0.6551 0.6276 89.16 5.57 −3.68 92.98 −1.45 −2.77 1472.43 85.5 20.9 97.5 0.5813 0.5704 65.80 54.91 −1.03 67.49 −13.12 −28.9315 78.23 89.5 11.7 97.4 0.7274 0.6445 66.25 56.62 −2.19 67.73 −12.85−29.26 16 78.97 90 10.9 97.2 0.8390 0.7894 69.54 51.05 −3.86 69.16−13.05 −27.92 17 79.90 89.2 12.8 97.6 0.7657 0.7429 69.05 51.84 −2.9569.51 −13.00 −27.46 18 78.47 88.9 11.6 97.5 0.8034 0.7384 68.33 52.70−3.55 69.20 −13.13 −28.33 19 78.52 90 10.9 97.4 0.5943 0.6632 68.9652.83 −3.82 68.80 −13.23 −28.39 20 78.50 89.7 12.2 97.2 0.6247 0.604467.57 52.82 −3.88 61.73 −12.98 −35.90 red blue blue Sample ref l red refa red ref b ref l ref a blue ref b 1 27.59 10.80 −1.47 21.88 −2.36−10.97 2 25.72 10.11 −0.17 22.39 −2.11 −9.76 3 24.20 11.35 −0.90 21.18−2.07 −12.11 4 23.45 13.46 0.39 19.26 −1.02 −12.89 5 25.99 18.31 5.8620.50 2.21 −16.48 6 24.49 17.07 4.52 20.43 1.04 −15.13 7 28.50 17.998.68 23.48 3.50 −15.45 8 27.73 15.53 8.78 22.78 4.02 −14.03 9 25.3015.88 6.94 20.37 1.16 −14.58 10 24.54 16.50 6.04 22.36 1.34 −13.46 1126.82 14.26 6.21 20.15 0.35 −13.63 12 28.02 2.57 −3.63 22.36 3.22 −12.6013 26.05 18.51 5.17 22.90 2.53 −15.26 14 29.60 13.63 7.93 20.82 1.69−15.28 15 24.83 16.47 6.64 27.63 −0.83 −4.90 16 22.19 16.84 2.82 21.452.06 −14.85 17 24.08 16.87 4.60 20.20 0.88 −15.88 18 26.74 16.58 4.9319.77 0.16 −16.20 19 24.11 17.22 4.86 19.77 1.53 −15.60 20 27.09 15.516.57 17.45 3.91 −14.12

Some effects of varying the particle size, concentration and thicknesscan be seen in Table 2 and in FIGS. 1 to 4. In FIGS. 1 and 4 theconcentration value is held at 60 whereas in FIGS. 2 and 3 the thicknessvalue is held at 4. One conclusion which can be drawn from FIGS. 1 to 4is the lower the particle size, the better.

Response Optimization

Response optimization was carried out to determine the optimal particlesize, concentration and thickness in relation to the data of thisexperiment.

The response optimization procedure requires targets to be met.Weightings can be applied which is useful if one parameter is moreimportant than another. However, for this exercise all responses wereconsidered of equal importance.

Parameters

Goal Lower Target Upper Weight Gloss Maximum 80 97 97 1 Haze Minimum 1 110 1 blue ref l Minimum 0 0 100 1 red ref l Minimum 0 0 100 1 red ref aMaximum 10 100 100 1 blue ref b Minimum −100 −100 −10 1

Global Solution

-   Size=95.9430-   Concentration=58.1313-   Thickness=2.59001

Predicted Responses

-   Gloss=88.0482 desirability=0.473421-   Haze=3.0247 desirability=0.775029-   Blue ref 1=22.1718 desirability=0.778282-   Red refl 1=26.2476 desirability=0.737524-   Red ref a=13.8736 desirability=0.043041-   Blue ref b=−12.5885 desirability=0.028761

The low desirability shown for the colour responses is in part due tothe fact that there is not a range of 100 to −100 in the raw data. Thusalthough desirable it is not possible even with prediction outside ofthe experimental design

In order to visualize the optimal values graphically, FIG. 5 shows eachof gloss, haze, blue ref 1, red ref 1, red ref a and blue ref b (asoutlined above) as a function of each of particle size, concentrationand thickness. The vertical dotted line under each of the threevariables indicates the optimal (Opt) values across all parameters. Ineach case, Optimal D is 0.25275.

It can be seen that size dominates all aspects but not in a linearfashion.

Therefore, in this experiment, the smallest particle size, ‘mid-range’concentration and nearly the lowest thickness used gives us one optimalposition. Other options are possible such as this coating on which filmwould not have to worry about haze so the optimisation would tend tofavour concentration. With a matt film the dominant factor is size.

Combination Printing

A coated product was made using the coating composition and proceduresdescribed above

This was then gravure printed. The print was various half tones from 10%ink through to 100% ink. The experiment looked for the lowest inktransfer to give a clear undisturbed print (no dots missing, no slurringof the cells etc.). The results are shown in Table 3.

TABLE 3 Sam- Size Concentration Fine tone gravure % ple nm % FTG % 2 41332.4 10% 6 413 45.4 <10%  9 96 38.9 10% 10 494 38.9 10% 11 295 28 10% 17295 38.9 <10% Values lower than 40 for FTG % are deemed very good.

Coefficient of Friction

The coefficient of friction was determined in accordance with thefollowing procedure.

1. Introduction:

1.1 The co-efficient of friction (slip) of film is a very importantproperty which can significantly affect printing press and packagingmachine performance.1.2 Test method is based on ASTM D1894.

2. Apparatus: 2.1 Instron Tensiometer Model 1011.

2.2 Slip platform with low friction pulley assembly mounted onto it.2.3 Sledge (6.5 cm×6.5 cm×0.5 cm, weight approx. 200 gms).2.4 Sledge string (70 cm long, non extensible).2.5 Cutting template (for sledge film sample) 20 cm×6.5 cm.

3. Reagents: None. 4. Test Method: 4.1 Instrument Set-Up 4.1.1 Switch onthe Instron.

4.1.2 Check the following settings are correct:—

Units=Metric Load Range=500 gms Transducer=5000 gms

Crosshead Speed=125 mm/minChart Recorder Speed=200 mm/min (20 mm×10)

Full Scale Deflection=500 gms Determination of the Co-efficient ofFriction (Slip)

4.1.3 Ensure surface of the metal platform is clean.4.1.4 Apply double sided tape across the width at each end of theplatform to hold film samples flat and crease free.

4.2 Procedure Film/Metal

4.2.1 Using the template, cut a sample of film (in the MD) and attach tothe sledge (using double-sided tape). Ensure that the film is free ofcreases or wrinkles.4.2.2 Ensure the top surface of the metal platform is clean.4.2.3 Pass the string around the low friction pulley and attach to thesledge.4.2.4 Place the sledge onto the platform, making sure there is a slightamount of slack in the string. The sledge should not be moved once ithas been placed on the platform.4.2.5 Start the chart recorder and press the “up” button for the“Instron” crosshead.4.2.6 On completion of the test, stop the chart and return the crossheadto the original position.4.2.7 Discard the film sample. A sample should not be used more thanonce.

Film/Film

4.2.8 Using the template, cut a sample of film (in the MD) and attach tothe sledge (using double-sided tape).4.2.9 Cut a sample approx. 15 cm (TD) and 35 cm (MD and attach to metalplatform using double-sided tape. Ensure that the film is free ofcreases or wrinkles.4.2.10 Here on follow steps 4.2.3. to 4.2.7.

5. Calculations:

5.1 The initial maximum reading from the chart is the staticco-efficient of friction (u s).

u s=Initial Maximum Value Recorded (gms)/Sled Weight (gms)

5.2 The average reading obtained during uniform sliding the two surfacesover each other is the dynamic co-efficient of friction (u d).

u d=Recorded Mean Value (gms)/Sled Weight (gms)

1. A laser writable labelling, packaging or security film incorporatinga composition comprising a laser writable pigment wherein at least 50%of the laser writable pigment particles have a particle size of lessthan about 1 micron.
 2. (canceled)
 3. The film according to claim 1,wherein the pigment undergoes a non-pyrolytic chemical or molecularidentifiable change in at least one observable or measurablecharacteristic on exposure to laser radiation.
 4. The film according toclaim 3, wherein the pigment undergoes a first non-pyrolytic chemical ormolecular identifiable change in at least one observable or measurablecharacteristic on exposure to a first laser radiation and wherein thepigment undergoes a second non-pyrolytic chemical or molecularidentifiable change in at least one observable or measurablecharacteristic on exposure to a second laser radiation.
 5. The filmaccording to claim 3, wherein the observable or measurablecharacteristic comprises the colour of the pigment.
 6. The filmaccording to claim 1, wherein the average particle size of the laserwritable pigment particles is about 100 nm or less.
 7. The filmaccording to claim 1, comprising an organic laser-writable pigment. 8.The film according to claim 7, comprising an unsaturated organiclaser-writable pigment.
 9. The film according to claim 8, wherein theorganic laser-writable pigment comprises at least one sp or sp²hybridized carbon atom.
 10. The film according to claim 9, wherein theorganic laser-writable pigment comprises ethylenic and/or acetylenicunsaturation.
 11. The film according to claim 10, comprising alaser-writable pigment comprising a diacetylene moiety.
 12. The filmaccording to claim 1, further comprising: a) indium tin oxide; and/or b)SABoTBA.
 13. The film according to claim 1, having a coating or layerwherein the coating or layer comprises the composition comprising thelaser writable pigment.
 14. The film according to claim 13, wherein thethickness of the layer or coating is about 10 microns or less.
 15. Thefilm according to claim 13, wherein the thickness is about 3 microns orless.
 16. The film according to claim 13, wherein the layer is a skinlayer.
 17. The film according to claim 1, having: a) a gloss (45°) ofgreater than 70 gloss units; or b) a gloss (45°) of greater than 85gloss units.
 18. The film according to claim 1, having a coefficient offriction of between about 0.4 and about 0.9.
 19. A package, label orsecurity product comprising the film according to claim
 19. 20. Apackaged, labelled or securitised product comprising the package, labelor security product of claim
 19. 21. (canceled)